This Engl Fireball Went On Strike!


This Engl Fireball head suffered a tube failure.  This sort of thing is usually not a big deal, but after the owner replaced the output tubes, a red “FAULT” light came on.  The amp played, but sounded a bit odd.  The Unbrokenstring Crew To The Rescue!

At first look, the rear panel is pretty simplistic.  However, let’s indulge in some Tech Porn and take a closer look.

OK, just a quick tour of the unit…  Here’s your typical IEC cord socket with integral mains fuse.

Footswitch jack functionality is straight-forward.

Interesting to note here is that the mix between the original signal (dry) and the stuff in the loop (effect) is set back here.  Since this control is on the back of the unit, it’s kinda ‘set and forget.’

So when this head reaches ‘end of life’ they want you to recycle it rather than just toss it in the waste bin.  Okay…

All you need to know is found here!

The output circuitry is very versatile; four, eight, sixteen ohms cabs, series and parallel, are no problem for this amp.

As the front panel is chrome, it’s a little tricky to make out the control nomenclature.  But very cool!

Not just gain, but Ultra Gain!  Is it a laundry soap?  Or more like A Clockwork Orange‘s ultra violence?

This amp has a ‘Power Tube Monitoring” circuit that indicates that a defective power tube has been isolated from the electrical power circuit.  This monitoring circuit protects the expensive components (rectifiers and power transformers) from further damage in the case of tube failure.  Oddly enough, something in the monitoring circuit went bad in this head, and now, known-good tubes still trigger the indicators.

Let’s take a look inside.  The quickest way inside is to enter through the back door.

With the back cover off, let’s unfasten the chassis from the amp cabinet.  This is a view of the bottom of the head.

These red LEDs add a little cheap bling to the appearance of the amp when it’s powered on.

Here’s another view of the bling LEDs.

The capacitors sticking through the chassis is kinda cool, but are a testimonial in favor of a good 3D CAD package.

These preamp tube shields are unique.  They clip through slots in the chassis itself.  A good squeeze liberates them.

Something new to me is the ENGL-branded preamp tubes.

Peeking around the backside of the front panel, we see the input jack and the end of the circuit board that carries the volume control and push buttons.  The braided sleeving over the power cable is a nice touch!

Here are the tone controls.  Note the flat ribbon cable sporting some hot glue as a strain relief.


Note the split ground planes in the circuit boards.

See the long metal straps that make electrical connection to the front panel LEDs, hanging under the circuit board?

The power transformer, sporting a sharp brass shield over the outer winding.

The output transformer lives under this steel shell.  It is attached to the circuit board, so all this comes off in order to remove the circuit board.  The weight of the output transformer makes the subsequent dis-assembly a little awkward.

The components we want to look at are on the other side of this large circuit board.

Many of the wires attached to the circuit board are ‘lap’ joints.  A little strip of RTV relieves the strain on the joint.

The low level circuitry is shielded by this steel sheet.  I’m removing it to get it out of the way.

Some of the lead dress will be loosened to allow the main circuit board to be inverted for service.

Rather than disturb a lot of solder joints, I just unfastened some of the smaller assemblies to free the main PCB.

This little resistor became a fuse, protecting the rest of the amp during tube failure.

This shows a little smoke, frozen in time.  When the smoke leaves a component, the component fails to work.  Thus, in the electronics world, we recognize “Magic Smoke” as the ‘stuff’ that makes electronics work.

The body of the burned resistor has been de-soldered.  Note the identical circuit, for the other output tube, to the right.

I’m using isopropyl alcohol for the cleanup on the circuit board.

While I’m at it, I’ll collect and save the Magic Smoke found on the chassis.  This can be used to resurrect other components.  If you don’t believe me, send me an email via the contact page so I know you are still reading this.

The affected portion of the protection circuit was repaired, and the other channel was repopulated with matching components so that they will behave exactly the same way if they are ever called into action in the future.

New tie wraps complete the restoration of the lead dress.

Now we’re pretty much back together.  This is a nice view of the chassis.

Remember the LED bling?  Well, here they are at work.  They are BRIGHT!

Both tubes are push/pulling and the bias is perfect.  The clean section is VERY clean on this amp!

With the lights down low, the bling is just a little understated.  I like it, and it sounds good!

Thanks for reading all the way to the end!

CONTACT INFO – David Latchaw EE

281-636-8626 voice or text